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Air speed is better on the stock RH10 than I thought it would be. 9whp is a lot going into that 20cfm. Which is to the point that it is not all CFM, I suspect the larger valve size removes a bottleneck.
RH4 To Narley Port Conversion Tubes
- Thread starter maaseyracer
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Air speed is better on the stock RH10 than I thought it would be. 9whp is a lot going into that 20cfm. Which is to the point that it is not all CFM, I suspect the larger valve size removes a bottleneck.
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If it was ported then its larger than 30mm now. Can you say how much larger it is and where?
Yes porting is very important. I sent some modified Axtell port specs to a 500 cc racer in the UK and he found a 7 hp increase (same size valves).
Brian's 500 (pre 1950 class)
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Fast Eddie
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Still 30mm Jim (like I clearly stated). Work was done around the valve throat only.If it was ported then its larger than 30mm now. Can you say how much larger it is and where?
Yes porting is very important. I sent some modified Axtell port specs to a 500 cc racer in the UK and he found a 7 hp increase (same size valves).
Brian's 500
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As far as speed is concerned, weight distribution can be more important than horsepower. If the front feels light, it will deter you from accelerating earlier when in corners.If it was ported then its larger than 30mm now. Can you say how much larger it is and where?
Yes porting is very important. I sent some modified Axtell port specs to a 500 cc racer in the UK and he found a 7 hp increase (same size valves).
Brian's 500 (pre 1950 class)
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Been working on these now for a while now and I think I am where I want to be with these. 3D printing the tube to get the size consistent proved to be a massive headache and hit the current limits of the technology. The success I had with these tubes required hand porting them to dimension which while very effective and easy for a one off, would have made these things very expensive to produce. Moving to just a floor we are able to take advantage of what is working in our favor with the larger ports.
A somewhat expected issue added another layer of complexity with these, which is getting the spacing with the frame figured out. I wanted to make sure with this design that carburetors did not become any more limited than they already are. With carbs like the Keihin CRS that I am running they just barely fit and I do not want to run into any issues with that. Port fit is really good and consistent with samples and the initial run I am sending over to Jim Schmidt, he will be taking this one over like the exhaust. These will be sold with a special gasket set and may require a sealant as well and I will update on the specifics of the sealant hopefully later this week.
While these are for the 32mm port heads I do have a version of this I am working on for a 30mm Norton head, which I have sent off to get samples along with some similar floors for other bikes. If all looks right with the 30mm floors they should follow be ready fairly soon.
If you want a set connect with Jim I imagine he will have them posted in the coming weeks.
A somewhat expected issue added another layer of complexity with these, which is getting the spacing with the frame figured out. I wanted to make sure with this design that carburetors did not become any more limited than they already are. With carbs like the Keihin CRS that I am running they just barely fit and I do not want to run into any issues with that. Port fit is really good and consistent with samples and the initial run I am sending over to Jim Schmidt, he will be taking this one over like the exhaust. These will be sold with a special gasket set and may require a sealant as well and I will update on the specifics of the sealant hopefully later this week.
While these are for the 32mm port heads I do have a version of this I am working on for a 30mm Norton head, which I have sent off to get samples along with some similar floors for other bikes. If all looks right with the 30mm floors they should follow be ready fairly soon.
If you want a set connect with Jim I imagine he will have them posted in the coming weeks.
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Just wondering if a recess has to be machined in the head to fit them in order to clear the frame (carbs)? btw, I have a Combat base and head will they fit this one (head)?Been working on these now for a while now and I think I am where I want to be with these. 3D printing the tube to get the size consistent proved to be a massive headache and hit the current limits of the technology. The success I had with these tubes required hand porting them to dimension which while very effective and easy for a one off, would have made these things very expensive to produce. Moving to just a floor we are able to take advantage of what is working in our favor with the larger ports.
A somewhat expected issue added another layer of complexity with these, which is getting the spacing with the frame figured out. I wanted to make sure with this design that carburetors did not become any more limited than they already are. With carbs like the Keihin CRS that I am running they just barely fit and I do not want to run into any issues with that. Port fit is really good and consistent with samples and the initial run I am sending over to Jim Schmidt, he will be taking this one over like the exhaust. These will be sold with a special gasket set and will most likely require a sealant as well and I will update on the specifics of the sealant hopefully later this week.
While these are for the 32mm port heads I do have a version of this I am working on for a 30mm Norton head, which I have sent off to get samples along with some similar floors for other bikes. If all looks right with the 30mm floors they should follow be ready fairly soon.
If you want a set connect with Jim I imagine he will have them posted in the coming weeks.
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No machining required. Drop in and go.
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If you look closely you can see that there is a teflon gasket surrounding the metal ring. The teflon stands proud of the ring a few thou to create a perfect seal to prevent vacuum leaks. The white teflon seal in the photo is a hand cut prototype and not a perfect fit - the perfect fit will happen when the teflon is sent out to be waterjet cut. These port floors started out with the Narley port floor and was then combined with the ring for easy installation (following the exhaust port floor idea).
Here's a view from the combustion chamber side. There is a little downward pressure exerted at the tip for sequrity when the ring is tightened down by the manifold as shown below. The raised intake port floor gives a better more gradual curve leading up to the valve seat for increased velocity
Below is a side view overlay showing how the port floor improves the curve and flow leading up to the intake valve.
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Will there be a 750 version?
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Working on it, depending on the port size some additional porting might be required. The 30mm port might work for some 750s, but I am not sure of 750 port sizes. With the tubes I was running a 30.6mm wide port and it was a really nice setup. This looks to be an even better setup.
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Looking forward to Jim's release of this for combat heads.
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Just waiting for the teflon gasket material to be shipped and waterjet cut into shape - about 3 weeks.
How thick is the Teflon gasket?
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The teflon gasket is 1/16" thick. The aluminum ring which is part of the intake shoe is several thousands of an inch less in thickness so the teflon gets clamped and creates a vacuum tight seal. The teflon is durable, heat resistant and reusable - it also helps serve as a heat insulator. The image shows the inside ring and the teflon gasket.
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Damn I skipped right over this when you first posted it.
Very early Commando 750 heads have just under 29mm intake openings at the manifold. Either that or my caliper doesn't work right anymore. The early Command head I have measures 28.7mm at the entrance. However, the early 750 Commando heads might not be your target audience. I also figure Knut will have some other measurement and point out my error. ha
I like this idea for the intake on a 750 head. Way easier than working with epoxy or welding to build up the floor. Should make for a nice charge.
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The early 750 ports are tough as they are already on the small side. I need to chat with Jim about these, however I suspect they will need some porting. Taking that port from 29 mm to 30.5mm wide or 32mm wide would make a very strong running engine. I was shocked at how good 30.5mm ran with the original tubes I made.
No error this time, Schwany. Atlas and G15 series had 1 -1/8" (28.575 mm) Monobloc and later Concentric carburettors and corresponding inlet ducts.
Early Commando models used basically the same cylinder head, and manifolds 06.2819 which provides a transition from 1-3/16 (30.16 mm) at carb to 1-1/8" at the head.
- Knut
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The small port 28.5mm 750 heads would need some port work with the raised floors. If we make them for the 750s then I plan on sending out port specs. But this is an excellent option because widening and raising the port along its length and giving it a cobrahead shape around the guide gives you a better downward angle into the cylinder. Its just a matter of doing the work and being careful - using a large diameter cartridge roll with a die grinder and measuring as you go - most importantly not going too far. You would widen and raise the port about 1mm on each side aiming for about a 30mm dia cross section.. See images below from my race manual.
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Yes that would make for a nice street bike ride.
My pre-Commando 750 head has intake ports over 31mm, but not quite 32mm. It was ported by Fred Barlow who was pretty good at it. It works well over carbureted with the right diameter and length intake manifolds and exhaust, and Jim's JS2 cam. I don't need to raise the intake floor in that head. I really don't want to spend a summer tuning it. Not young enough anymore. he he
For the early Commando 750 people that might be interested in the port floor insert, the port work Jim Schmidt mentions is pretty easy to do around the guide near what I call the bowl entrance in my laymen terms. Changing the length of the venturi inside diameter is harder without some kind of small bore cutting tool. I'm doing it all with my fingers when I get the urge to do it with my spare early Commando head. It takes forever doing it like I do, but you machinist guys will have no trouble doing it faster. I won't be going larger than 30.5mm at the entrances to the venturi. If I ever end up using that spare Commando 750 head, I think I would use smaller carburetors. The 33mm Keihin CRS carburetors would be a good choice.
Hopefully I have not pissed anyone off today with my BS. It's early and Thanksgiving in the USA.
